Diamond-like carbon films with low dielectric constant and high mechanical strength

ABSTRACT

The present invention discloses a method including: providing a substrate; and sequentially stacking layers of two or more diamond-like carbon (DLC) films over the substrate to form a composite dielectric film, the composite dielectric film having a k value of about 1.5 or lower, the composite dielectric film having a Young&#39;s modulus of elasticity of about 25 GigaPascals or higher. 
     The present invention further discloses a structure including: a substrate; a porous diamond-like carbon (DLC) film located over the substrate; an opening located in the porous DLC film; and a conductor located in the opening.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to the field of semiconductor integratedcircuit (IC) manufacturing, and more specifically, to an electricallyinsulating material with low dielectric constant and high mechanicalstrength and a method of making such an electrically insulatingmaterial.

2. Discussion of Related Art

In 1965 Gordon Moore observed that the pace of technology innovationwould result in a doubling of the number of devices per unit area on anIC chip approximately every 18 months. Over the ensuing decades, thesemiconductor industry has adhered closely to the schedule projected byMoore's Law for improving device density.

Maintaining such an aggressive schedule for each device generation hasrequired continual enhancements at the corresponding technology node.Devices on a chip are typically fabricated in a substrate fromsemiconducting material, such as silicon, and electrically insulatingmaterial, such as silicon oxide or silicon nitride. Subsequently, thedevices may be wired with electrically conducting material, such ascopper. The electrically conducting material may be stacked in layersthat are separated vertically and horizontally by electricallyinsulating material.

On the one hand, the additive processes of ion implantation, annealing,oxidation, and deposition had to be improved to produce the requisitedoping profiles and film stacks across the chip. On the other hand, thesubtractive processes of photolithography and etch also had to beenhanced to shrink the features across the chip while maintainingpattern fidelity.

Photolithography was able to keep up with the reduction in the criticaldimension (CD) needed for each device generation. However, improving theresolution that could be achieved often required compromising the depthof focus (DOF). As a result, the smaller DOF made it necessary tominimize the topography across the substrate in which the device wasbeing formed. Planarization of the surface of the substrate withchemical-mechanical polish (CMP) became necessary to fabricate advanceddevices.

In order to improve device density, both the transistor in the front-endof semiconductor processing and the wiring in the back-end ofsemiconductor processing have to be scaled down. The scaling of thetransistor and the scaling of the wiring must be carefully balanced toavoid degrading performance or reliability of the chip.

The switching speed of the transistor may be adversely impacted by anexcessively large resistance-capacitance (RC) product delay in thewiring. Resistance in the wiring may be reduced by using electricallyconducting material with low resistivity. Capacitance in the wiring maybe reduced by using electrically insulating material with low dielectricconstant (k).

However, the electrically insulating material with low dielectricconstant must also have high mechanical strength to withstand the rigorsof front-end and back-end of semiconductor processing, as well as, thepackaging steps.

Thus, what is needed is an electrically insulating material with lowdielectric constant and high mechanical strength and a method of makingsuch an electrically insulating material.

BRIEF DESCRIPTION OF THE DRAWINGS

FIGS. 1 A-F are illustrations of a cross-sectional view of an embodimentof a method of forming an electrically insulating material with lowdielectric constant and high mechanical strength according to thepresent invention.

FIG. 1 F is also an illustration of a cross-sectional view of astructure including a dielectric having low dielectric constant and highmechanical strength.

DETAILED DESCRIPTION OF THE PRESENT INVENTION

In the following description, numerous details, such as specificmaterials, dimensions, and processes, are set forth in order to providea thorough understanding of the present invention. However, one skilledin the art will realize that the invention may be practiced withoutthese particular details. In other instances, well-known semiconductorequipment and processes have not been described in particular detail soas to avoid obscuring the present invention.

The present invention describes a method of forming a diamond-likecarbon film with low dielectric constant and high mechanical strength,such as for insulating interconnects on a chip. Various embodiments ofthe method of forming a diamond-like carbon film are shown in FIGS. 1A-F.

The present invention further describes a structure having adiamond-like carbon film with low dielectric constant and highmechanical strength, such as for an interlayer dielectric film on achip. Various embodiments of the structure having a diamond-like carbonfilm are shown in FIG. 1 F.

As shown in an embodiment of the present invention in FIG. 1 A, a device95 may be formed in a substrate 90. The device 95 may be active orpassive. The device 95 may include a memory device or a logic device.The substrate 90 may include a semiconducting material, such as silicon.

In an embodiment of the present invention, the substrate 90 may becovered with an etch stop layer 100. The etch stop layer 100 may have athickness selected from a range of about 20-60 nanometers (nm).

In an embodiment of the present invention, a barrier layer (not shown)may be formed over the etch stop layer 100 to prevent any intermixing orreaction.

Next, an interlayer dielectric (ILD) 110 film of diamond-like carbon(DLC) may be formed over the etch stop layer 100. In an embodiment ofthe present invention, the ILD 110 film may include a compositedielectric film, such as the DLC. The DLC in the ILD 110 film may have athickness selected from a range of about 100-500 nm.

In an embodiment of the present invention, the ILD 110 film may beformed by sequentially stacking two or more layers of DLC films toproduce a composite dielectric film having appropriate properties and adesired thickness. The layers that are sequentially stacked to form thecomposite dielectric film may vary in thickness, crystallinity, andporosity.

The first layer of the stack is at the bottom of the ILD 110 film. Theodd layers may include the first layer, the third layer, the fifthlayer, and so on. The even layers may include the second layer, thefourth layer, the sixth layer, and so on. In an embodiment of thepresent invention, certain layers, such as the odd layers, may have nopores while other layers, such as the even layers, may have pores. Inanother embodiment of the present invention, an odd layer is at the topof the ILD 110 film.

In an embodiment of the present invention, the DLC may be formed with achemical vapor deposition (CVD) process. In the CVD process, precursormolecules in a gas phase may be dissociated, or activated, by an energysource to form active species, such as reactive radicals, ions, oratoms. The active species in the gas phase may react and condense over asolid surface, such as the etch stop layer 100, to form the DLC.

In an embodiment of the present invention, the CVD process may occur atatmospheric pressure (about 760 Torr) or higher with an energy sourcethat may include a combustion flame source, such as an oxyacetylenetorch source or a plasma torch source. The plasma torch source mayinclude a Direct Current (DC) plasma arc jet source.

In an embodiment of the present invention, the CVD process may occur atatmospheric pressure (about 760 Torr) or lower with an energy sourcethat may include a thermal source, such as a hot filament (HF) source.The HF source may include a single filament or multiple filaments.

In an embodiment of the present invention, the CVD process may occur atatmospheric pressure (about 760 Torr) or lower with an energy sourcethat may include an electron or ion bombardment source, such as anelectrical discharge source or a plasma source.

In an embodiment of the present invention, the ILD 110 film may beformed from DLC by using a plasma-enhanced CVD (PECVD) process. Theplasma source may include a radio frequency (RF) plasma source, amicrowave (MW) plasma source, an electron cyclotron resonance (ECR)plasma source, a Direct Current (DC) plasma source, or a laser plasmasource.

In an embodiment of the present invention, the RF plasma source may begenerated by radiation with a frequency of about 13.56 MegaHertz (MHz).In another embodiment of the present invention, the RF plasma source mayinclude an inductively-coupled plasma (ICP) source.

In an embodiment of the present invention, a negative substrate bias ofabout 40-800 volts DC may be used with the RF plasma source. In anotherembodiment of the present invention, a negative substrate bias of about800-3,500 volts DC may be used with the RF plasma source. The substratebias may be a function of the RF plasma power and the pressure in thereactor. The substrate bias may also depend on the geometry and thedimensions of the reactor. In an embodiment of the present invention,the reactor, or deposition tool, may include parallel plates.

In an embodiment of the present invention, the MW plasma may begenerated by radiation with a frequency of about 2.45 GigaHertz (GHz).In another embodiment of the present invention, the MW plasma may begenerated by radiation with a frequency of about 915 MHz.

In an embodiment of the present invention, the laser plasma may begenerated by radiation with an ultraviolet (UV) wavelength from anexcimer laser with multiple pulses.

The process to form the DLC may be selected to produce desired structureand properties for the ILD 110 film. The process parameters fordeposition of the ILD 110 film may include source gas flow rate,substrate temperature, reactor pressure, and plasma power (or plasmapower density).

In an embodiment of the present invention, the deposition of the ILD 110film may include a source gas flow rate of about 50-200 standard cubiccentimeters per minute (SCCM). In another embodiment of the presentinvention, the source gas flow rate may be about 200-800 SCCM. In stillanother embodiment of the present invention, the source gas flow ratemay be varied as a function of time.

In an embodiment of the present invention, the deposition of the ILD 110film may include a substrate temperature of about 200-250 degreesCentigrade. In another embodiment of the present invention, thedeposition of the ILD 110 film may include a substrate temperature ofabout 250-400 degrees Centigrade. In still another embodiment of thepresent invention, the deposition of the ILD 110 film may include asubstrate temperature of about 400-850 degrees Centigrade. In yetanother embodiment of the present invention, the deposition of the ILD110 film may include a substrate temperature of about 850 degreesCentigrade or higher.

In an embodiment of the present invention, the deposition of the ILD 110film may include a pressure of about 0.001-20 Torr. In anotherembodiment of the present invention, the deposition of the ILD 110 filmmay include a reactor pressure of about 20-250 Torr. In still anotherembodiment of the present invention, the deposition of the ILD 110 filmmay include a reactor pressure of about 250-760 Torr. In yet anotherembodiment of the present invention, the deposition of the ILD 110 filmmay include a reactor pressure of about 760 Torr or higher.

In an embodiment of the present invention, the deposition of the ILD 110film may include a plasma power of about 1-10 kilowatts (kW). In anotherembodiment of the present invention, the plasma power may be about10-100 kW. In an embodiment of the present invention, the plasma powermay be pulsed on and off as a function of time. In another embodiment ofthe present invention, the plasma power may be varied as a function oftime.

In an embodiment of the present invention, the plasma power density maybe about 0.1-0.5 Watts per square centimeter (W/cm2). In anotherembodiment of the present invention, the plasma power density may beabout 0.5-2.5 W/cm2.

Nucleation and growth of the lattice of the DLC may depend on theunderlying layer over which the ILD 110 film is being formed. In anembodiment of the present invention, the underlying layer may be theetch stop layer 100. In another embodiment of the present invention, theunderlying layer may be the substrate 90. In still another embodiment ofthe present invention, the underlying layer may be the barrier layer(not shown). If the underlying layer includes silicon, an intermediatelayer such as beta-SiC, with a thickness such as several nanometers, maybe formed.

In an embodiment of the present invention, the underlying layer may bepretreated prior to deposition. In another embodiment of the presentinvention, plasma treatment may be used to increase the roughness of thesurface of the underlying layer to increase the deposition rate.

The deposition rate of the DLC may depend on the process parameters. Inan embodiment of the present invention, the deposition rate for the ILD110 film may be about 0.5-4.0 nm/minute. In another embodiment of thepresent invention, the deposition rate for the ILD 110 film may be about4.0-30.0 nm/minute. In still another embodiment of the presentinvention, the deposition rate for the ILD 110 film may be about30.0-250.0 nm/minute.

In an embodiment of the present invention, the process to form the ILD110 film may be alternated between a deposition step to form a latticefor the DLC and a modification step to change the lattice of the DLC.The process of alternating between the deposition step and themodification step may be repeated until a desired thickness for the ILD110 film is achieved. The ILD 110 film may include a compositedielectric film, such as the DLC. The DLC in the ILD 110 film may have athickness selected from a range of about 100-500 nm.

In an embodiment of the present invention, the deposition step and themodification step may occur in the same chamber of the deposition tool.In another embodiment of the present invention, the deposition step andthe modification step may occur in separate chambers of the depositiontool.

The characteristics of the DLC in the ILD 110 film may be modified bychoice of precursors in the source gas stream for the deposition step.Atomic carbon may be provided by a carbonaceous source. In an embodimentof the present invention, the carbonaceous source may include ahydrocarbon, R—H. In another embodiment of the present invention, thecarbonaceous source may include a substituted hydrocarbon, X—R—H. Instill another embodiment of the present invention, the carbonaceoussource may include a chlorohydrocarbon, Cl—R—H. In yet anotherembodiment of the present invention, the carbonaceous source may includea chloromethane, such as CCl4, CHCl3, or CH2Cl2.

Additives may be included in the source gas stream for the depositionstep if desired. Additives in the source gas stream for the depositionstep may include nitrogen or Argon. In an embodiment of the presentinvention, a small amount of nitrogen, such as about 2.5 parts pertrillion (ppt) may increase the deposition rate of the DLC in the ILD110 film by a factor of 2. In another embodiment of the presentinvention, nitrogen may reduce intrinsic stress in the DLC in the ILD110 film. The intrinsic stress in the DLC is usually compressive.

Additives may change the morphology or texture of the DLC in the ILD 110film by affecting the kinetics of the active species (such as thereactive radicals, ions, or atoms) for adsorption to, desorption from,and diffusion over the surface of the underlying layer. In an embodimentof the present invention, additives may affect the degree ofcrystallinity of the DLC. The DLC may be separated by grain boundariesinto clusters, regions, or domains, of various sizes that aresingle-crystalline, nanocrystalline, polycrystalline, or amorphous. Inanother embodiment of the present invention, additives may introducevoids and facets.

In an embodiment of the present invention, the structure and theproperties of the DLC, as a function of depth (z-position) in the ILD110 film, may be optimized by customizing, or tailoring, the processparameters in situ. In another embodiment of the present invention, theprocess parameters may be changed in discrete steps during formation ofthe ILD 110 film. In still another embodiment of the present invention,the process parameters may be varied continuously during formation ofthe ILD 110 film.

In an embodiment of the present invention, the process parameters may beselected to favor formation of sp3 bonds, with a tetrahedralcoordination, between carbon atoms to produce a 3-dimensional network ofpredominantly diamond forms of carbon in the structure of the ILD 110film.

In another embodiment of the present invention, the process parametersmay be selected to favor formation of sp2 bonds, or double bonds, with aplanar coordination, between carbon atoms to produce weakly-bonded2-dimensional networks of predominantly non-diamond forms of carbon,such as graphite, in the structure of the ILD 110 film.

In still another embodiment of the present invention, the processparameters may be selected to favor formation of aromatic carbon rings,or multi-membered carbon rings. The multi-membered carbon rings may bemostly six-membered carbon rings, with some five-membered carbon ringsand some seven-membered carbon rings.

In yet another embodiment of the present invention, the processparameters may be selected to favor formation of sp1 bonds.

In an embodiment of the present invention, the ILD 110 film may bemodified by creating pores in the lattice of the DLC. Each pore mayinclude one or more discontinuities, voids, and defects. The defects mayinclude interstitials and vacancies. The interstitials refer to thecarbon atoms that have been displaced from the sites in the lattice. Thevacancies refer to the sites in the lattice that have not been occupiedby any carbon atom. The defects may also include microtwins,dislocations, stacking faults, and amorphous regions.

The DLC in the ILD 110 film may be modified by choice of precursors inthe source gas stream for the modification step. The modification stepmay include etching. In an embodiment of the present invention, etchingmay result from atomic hydrogen provided by a hydrogen source, such ashydrogen gas, H2. Atomic hydrogen in the plasma stabilizes the diamondforms of carbon by selectively etching the non-diamond forms of carbon.The non-diamond forms of carbon may include graphite, aromatic carbonrings, multi-membered carbon rings, and defective carbon materials. Inan embodiment of the present invention, atomic hydrogen may etch thenon-diamond forms of carbon about 2-5 times faster than the diamondforms of carbon.

In an embodiment of the present invention, etching may result fromatomic oxygen. In another embodiment of the present invention, etchingmay result from molecular oxygen. In still another embodiment of thepresent invention, etching may result from atomic fluorine. Additivesmay also be included in the source gas stream for the modification stepif desired.

The composition of the source gas stream may be varied between thedeposition step and the modification step to achieve the desiredmaterial properties for the DLC in the ILD 110 film. The relativedurations of the deposition step and the modification step may also beadjusted.

In an embodiment of the present invention, the composition of the sourcegas stream may be varied between a higher R—H/H2 ratio for thedeposition step and a lower R—H/H2 ratio for the modification step. Ahigher R—H/H2 ratio favors formation of sp3 bonds, with a tetrahedralcoordination, between carbon atoms to produce diamond forms of carbon. Alower R—H/H2 ratio favors formation of sp2 bonds, with a planarcoordination, between carbon atoms to produce non-diamond forms ofcarbon. The non-diamond forms of carbon may include graphite, aromaticcarbon rings, multi-membered carbon rings, and defective carbonmaterials.

In an embodiment of the present invention, R may be CH3 so R—H may beCH4 or methane. In an embodiment of the present invention, thedeposition step may include a source gas, with a small amount of CH4 inH2 by volume, for a duration of about 60 seconds to form a thin layerhaving a high concentration of non-diamond forms of carbon, as well as,defects. In an embodiment of the present invention, the modificationstep may include a source gas of about 100% H2 by volume for a durationof about 30 seconds to selectively etch the non-diamond forms of carbonwithin the lattice of the DLC. The non-diamond forms of carbon that maybe deposited and etched may include graphite, aromatic carbon rings,multi-membered carbon rings, and defective carbon materials. The defectsmay include interstitials and vacancies. The defects may also includemicrotwins, dislocations, stacking faults, and amorphous regions.

In an embodiment of the present invention, the source gas for depositionincludes about 0.1-1.0% CH4/H2 by volume. In another embodiment of thepresent invention, the source gas for deposition includes about 1.0-2.0%CH4/H2 by volume. In still another embodiment of the present invention,the source gas for deposition includes about 2.0-5.0% CH4/H2 by volume.

The properties of the ILD 110 film may include the dielectric constant,or k value, and the Young's modulus of elasticity. The DLC, in the bulkand without pores, may have a k value of about 5.5-6.7 and a Young'smodulus of elasticity of about 800-1,200 GPa. In an embodiment of thepresent invention, the DLC may be used to form an ILD 110 film withappropriate properties if pores 112 may be introduced into the DLC tosufficiently reduce the effective k value for the ILD 110 film whileadequately maintaining the mechanical strength for the ILD 110 film.

The pores 112 may be created in-situ in the ILD 110 film. The pores 112may be filled with a material, such as a gas, with a low k value. In anembodiment of the present invention, the gas may include air with a kvalue of about 1.0. In another embodiment of the present invention, thegas may include hydrogen. In another embodiment of the presentinvention, the gas may include nitrogen.

The effective k value of the ILD 110 film depends upon the nominal kvalue of the bulk material forming the ILD 110 film and the nominal kvalue of the material, if present, filling the pores 112, weighted bythe total porosity of the ILD 110 film. The effective k value for theILD 110 film should be reduced as the design rules for the device 95 aredecreased.

In an embodiment of the present invention, the ILD 110 film may have a kvalue of about 2.5 or lower. In another embodiment of the presentinvention, the ILD 110 film may have a k value of about 2.0 or lower. Instill another embodiment of the present invention, the ILD 110 film mayhave a k value of about 1.5 or lower. The k value may be determined bymeasuring capacitance on a parallel-plate electrical structure.

The ILD 110 film should possess high mechanical strength so as towithstand the stresses induced by processing, such as at the waferlevel, the chip level, and the package level. Young's modulus ofelasticity is a measurement of the mechanical strength of a material. Inan embodiment of the present invention, the ILD 110 film may have aYoung's modulus of elasticity of about 25 GPa or higher.

Shear strength is another measurement of the mechanical strength of amaterial. The shear strength of the ILD 110 film should be sufficient towithstand the CMP process that may be used to planarize the conductorlayer 170, as shown in an embodiment in FIG. 1 F. In an embodiment ofthe present invention, the ILD 110 film may have a shear strength ofabout 15 GPa or higher.

Fracture toughness is yet another measurement of the mechanical strengthof a material. In an embodiment of the present invention, the ILD 110film may have a high fracture toughness.

The mechanical strength of the ILD 110 film may depend upon severalfactors, such as the total porosity, the local porosity, the pore 112size (such as, the equivalent diameter), and the pore 112 sizedistribution across the ILD 110 film. The mechanical strength of the ILD110 film may also depend upon the density of the ILD 110 film.

Total porosity is the pore fraction by volume and may vary from zero toone. In an embodiment of the present invention, the total porosity ofthe ILD 110 film may be selected from a range of about 0.15-0.30. Inanother embodiment of the present invention, the total porosity of theILD 110 film may be selected from a range of about 0.30-0.45. In stillanother embodiment of the present invention, the total porosity of theILD 110 film may be selected from a range of about 0.45-0.60. In yetanother embodiment of the present invention, the total porosity of theILD 110 film may be selected from a range of about 0.60-0.75.

In an embodiment of the present invention, a high total porosity, suchas about 0.60-0.75, may reduce mechanical strength and barrier layercoverage. In another embodiment of the present invention, a high totalporosity, such as about 0.60-0.75, may increase surface roughness andline-edge roughness (LER).

The local porosity of the ILD 110 film may vary for a given totalporosity. In an embodiment of the present invention, the local porositymay vary by location (x-position and y-position) within the plane of theILD 110 film. In another embodiment of the present invention, the localporosity may vary as a function of depth (z-position) in the ILD 110film.

The pores 112 in the ILD 110 film may be closed, interconnected, oropen. The closed pores may include voids with internal surfaces that arespread around a nominal center. In an embodiment of the presentinvention, closed pores may be small with an equivalent diameter that isselected from a range of about 2-6 nm. In another embodiment of thepresent invention, closed pores may be medium with an equivalentdiameter that is selected from a range of about 6-18 nm. In stillanother embodiment of the present invention, closed pores may be largewith an equivalent diameter that is selected from a range of about 18-55nm.

The interconnected pores may include two or more closed pores that havemerged together. In an embodiment of the present invention, the poresmay start transitioning from closed pores to interconnected pores at atotal porosity of about 0.30 or higher. In another embodiment of thepresent invention, the pores may start transitioning from closed poresto interconnected pores at a total porosity of about 0.45 or higher.

The open pores may include pores that have intersected external surfacesof the ILD 110 film. Open pores may trap contaminants, especially thosethat are liquid or gaseous. The contaminants may affect function,operation, performance, or reliability of the device 95 in the substrate90.

The open pores may also reduce the surface area for adhesion at aninterface between the ILD 110 film and an underlying or overlying layer.The reduced surface area may decrease interfacial bonding strength andmay result in delamination or cracking, especially when a mismatch incoefficient of thermal expansion (CTE) exists among the materials in thevicinity of the interface.

In an embodiment of the present invention, the CTE may be about 1-3parts per million per degree Kelvin (ppm/K) for the DLC in the ILD 110film, about 2-7 ppm/K for the substrate 90 and the etch stop layer 100,and about 12-23 ppm/K for the conductor layer 170. In another embodimentof the present invention, the CTE of the DLC in the ILD 110 film may bematched closely with the CTE for the substrate 90 and the etch stoplayer 100.

An embodiment of a variation of a via-first process flow for a dualDamascene scheme will be described next. However, different embodimentsof the present invention are compatible with other process flows, suchas a variation of a trench-first process flow for a dual Damascenescheme.

After formation of DLC for the ILD 110 film, the processes ofphotolithography and etch are used to pattern a via 127, as shown in anembodiment in FIGS. 1 A-B. A radiation-sensistive material, such as avia-layer photoresist 120, may be applied over the ILD 110 film. Then, aportion of the via-layer photoresist 120 is exposed to radiation of anappropriate wavelength and dose. The exposure is performed in an imagingtool, such as a wafer stepper or a wafer scanner. A via-layer reticlemay be placed in the optical path of the radiation to determine theportion of the via-layer photoresist 120 that is to be exposed. Exposureis followed by development of the via-layer photoresist 120 to create avia-layer mask.

The via-layer mask includes a via feature 125 that corresponds to theexposed portion of the via-layer photoresist 120, as shown in anembodiment in FIG. 1 A. The shape and critical dimension (CD) of the viafeature 125 in the via-layer photoresist 120 is derived from a design onthe via-layer reticle. In an embodiment of the present invention, thephotoresist 120 may have a thickness of about 100 nm and the via feature125 may have a CD of about 65 nm.

The via feature 125 patterned in the via-layer photoresist 120 may betransferred into the ILD 110 by a dry etch process, as shown in anembodiment in FIG. 1 B. A dry etch process, such as a plasma etchprocess or a reactive ion etch process (RIE), may be used to etch a via127 completely through the ILD 110 film. The formation of the via 127may involve precleans and postcleans associated with the etch. The etchstop layer 100 under the ILD 110 film allows a longer over-etch to cleanout the bottom of the via 127 without breaking through and damaging theunderlying conductor 95.

High directionality is desired for the via 127 etch when the narrowestportion of the via 127 has a large aspect ratio (depth:width), such asabout 6:1 or greater. In one embodiment, a high density plasma, such asan RF ICP, may be used.

The dry etch of the ILD 110 film to form the via 127 may be performedwith a gas mixture. The gas mixture for etching an ILD 110 film formedfrom DLC may include oxygen, O2. Other gases that may be used for via127 etch include H2O. The etch rate of the ILD 110 film may be selectedfrom a range of about 15-120 nm/minute.

The etch selectivity of the ILD 110 film to the via-layer photoresist120 may be higher than about 3:1. If the etch selectivity is notsufficiently large, additional processing complexity may be required,such as including a hard mask (not shown) that will not be eroded duringdry etch of the ILD 110 film.

After via 127 etch, the via-layer photoresist 120 is removed. Ifdesired, the via 127 etch and the strip of the via-layer photoresist 120may be done sequentially in an integrated tool.

The etch stop layer 100 is thick enough to prevent the via 127 etch frombreaking through to damage the underlying device 95 in the substrate 90.

After formation of the via 127, the processes of photolithography andetch are used to pattern a trench. A bottom anti-reflective coating(BARC) 130 may be formed over the ILD 110 film and in the via 127, asshown in an embodiment in FIG. 1 C. Then, a trench-layer photoresist 140is applied over the BARC 130. The BARC 130 will minimize any exposureproblem in the vicinity of the via 127 that may be caused by swing-curveeffects from the thickness variation in the trench-layer photoresist 140by light-scattering effects from the step-height change in the ILD 110film. The BARC 130 also minimizes further etch of the via 127 during thesubsequent etch of the trench.

Then, the trench-layer photoresist 140 is exposed using radiation of theappropriate wavelength and dose. The exposure is performed in an imagingtool, such as a wafer stepper or a wafer scanner, and modulated by atrench-layer reticle. Exposure is followed by development of a trenchfeature 145 in the trench-layer photoresist 140.

The trench feature 145 in the trench-layer photoresist 140 issuperimposed over the via 127 etched into the ILD 110 film. The shapeand CD of the trench feature 145 is derived from a design on thetrench-layer reticle. In an embodiment of the present invention, theBARC 130 may have a thickness of about 35 nm, the photoresist 140 mayhave a thickness of about 100 nm, and the trench feature 145 may have aCD of about 65 nm.

A dry etch process, such as a plasma etch process or an RIE process, maybe used to partially etch the ILD 110 film to form a trench over the via127, as shown in an embodiment in FIG. 1 D. High directionality isdesired for the trench etch when the narrowest portion of the trench—viaopening 147 has a large aspect ratio (depth:width), such as about 6:1 orgreater. In one embodiment, a high-density plasma, such as an RF ICP,may be used for the trench etch.

The dry etch of the ILD 110 film to form the combined trench—via opening147 may be performed with a gas mixture. The gas mixture for etching anILD 110 film formed from DLC may include oxygen, O2. Other gases thatmay be used for trench etch include H2O. The etch rate of the ILD 110film may be selected from a range of about 15-120 nm/minute.

The etch selectivity of the ILD 110 film to the trench-layer photoresist140 may be higher than about 3:1. If the etch selectivity is notsufficiently large, additional processing complexity may be required,such as including a hard mask (not shown) that will not be eroded duringdry etch of the ILD 110 film.

After etching the trench—via opening 147 in the ILD 110 film, thetrench-layer photoresist 140 and the underlying BARC 130 are removed. Ifdesired, the trench etch and the strip of the trench-layer photoresist140 and the BARC 130 may be done sequentially in an integrated tool.

Then, the portion of the etch stop layer 100 underlying the trench—viaopening 147, as shown in an embodiment in FIG. 1 D, is removed, such asby a dry etch. The underlying conductor 95 should not be damaged by theremoval of the portion of the etch stop layer 100 below the trench—viaopening 147.

As shown in an embodiment in FIG. 1 E, a barrier layer 115 is formedover the ILD 110 film and in the trench—via opening 147. Copper may beused for the conductor layer 170 to be formed later in the trench—viaopening 147. Copper has a high diffusivity so the barrier layer 150 mustencapsulate the sides and the bottom of the trench—via opening 147 toprevent diffusion of Copper into the ILD 110 film and the deviceconnected to the underlying conductor 95. Otherwise, Copper mayintroduce mid-gap states into the semiconductor material forming thedevice and degrade carrier lifetime.

The barrier layer 115 may be formed from a metal, including a refractivemetal, such as Tantalum (Ta), or an alloy, such as Titanium-Tungsten(TiW), or a ceramic, such as Tantalum-Nitride (TaN),Tantalum-Silicon-Nitride (TaSiN), Titanium-Nitride (TiN), orTungsten-Nitride (WN). The barrier layer 150 may have a thicknessselected from a range of about 5-20 nm.

In one embodiment, the barrier layer 115 may include a lower layer ofTaN to adhere to the underlying ILD 110 film and an upper layer of Ta toadhere to the overlying seed layer 150. A barrier layer 115 formed froma Ta/TaN bilayer may have a total thickness selected from a range ofabout 8-15 nm.

High directionality is desired for forming the barrier layer 115,especially when the narrowest portion of the trench—via opening 147 hasa large aspect ratio (depth:width), such as about 6:1 or greater. Thetechnique of ionized physical vapor deposition (I-PVD) may be used toform a material with better step coverage than other techniques, such ascollimation sputtering or long-throw sputtering (LTS).

In certain cases, a MOCVD process may be used to form the barrier layer115. Alternatively, the barrier layer 115 may be formed usingatomic-layer deposition (ALD), especially for a thickness of about 10 nmor less. ALD may provide good step coverage and good thicknessuniformity even while permitting the use of a low depositiontemperature, such as of about 200-400 degrees Centigrade.

When the trench—via opening 147 is to be filled later by electroplatinga conductor layer 170, a seed layer 150 should first be formed over thebarrier layer 115, as shown in an embodiment in FIG. 1 E. In order toserve as a base for electroplating, the seed layer 150 must beelectrically conductive and continuous over the barrier layer 115.Adhesion loss of the seed layer 150 from the underlying barrier layer115 should be prevented. Interfacial reaction of the seed layer 150 withthe underlying barrier layer 115 should also be prevented.

The seed layer 150 may be formed from the same or different material asthe conductor layer 170 to be formed later. For example, the seed layer150 may include a metal, such as Copper, or an alloy. The seed layer 150may have a thickness selected from a range of about 10-20 nm.

The seed layer 150 may be deposited by I-PVD, especially when theconductor layer 170 is to be formed later by electroplating. If desired,the barrier layer 115 and the seed layer 150 may be sequentiallydeposited in a tool, without breaking vacuum, so as to prevent formationof an undesirable interfacial layer between the barrier layer 115 andthe seed layer 150.

When the conductor layer 170 is to be subsequently formed by PVD, bettermaterial properties and surface characteristics may be achieved for theconductor layer 170 if the seed layer 150 is formed using CVD. The seedlayer 150 may also be formed with ALD or electroless plating.

Next, the trench—via opening 147 may be filled with a conductor layer170 to make electrical contact with the underlying device 95, as shownin an embodiment in FIG. 1 F. The conductor layer 170, such as a metal,may be formed over the seed layer 150 by an electrochemical process,such as electroplating or electrofilling. The conductor layer 170 mayhave a thickness that provides an overburden of about 400 nm above theILD 110 film.

In other embodiments, the conductor layer 170 may be formed with a PVDprocess or a CVD process. A PVD process or a CVD process may beparticularly advantageous when forming the conductor layer 170 over atrench—via opening 147 that has a large aspect ratio (depth:width), suchas about 6:1 or greater. A PVD process usually has a lowerCost-of-Ownership (CoO) than a CVD process. In some cases, a MOCVDprocess may also be used.

The conductor layer 170 may be treated after being formed to modify itsmaterial properties or surface characteristics. The treatment mayinclude a rapid thermal anneal (RTA) process after deposition to modifyor stabilize grain size. For example, Copper that has been formed byelectroplating may have a grain size of about 50-10,000 nm, dependingupon the thickness, deposition conditions, and anneal conditions. Alarger grain size usually corresponds to a lower resistivity which ismore desirable. For example, Copper may have a resistivity of about1.7-2.5 micro-ohm-centimeter (uohm-cm) at 20 degrees Centigrade.

A as shown in an embodiment in FIG. 1 F, a chemical-mechanical polishing(CMP) process may be used to remove the overburden of the conductorlayer 170 and the portion of the barrier layer 115 over an upper surface117 of the ILD 110 film. The CMP process to create an inlaidinterconnect 175 in the trench—via opening 147 may be optimizeddepending upon the polish rates of different materials. Polishselectivity to different materials may be optimized by changing theproperties of the polish pad, the properties of the polish slurry, andthe parameters of the polish tool.

The process of CMP combines abrasion and dissolution to flatten andsmoothen surface relief. Abrasion occurs when higher portions of thesurface contact a pad and abrasive particles in a slurry and becomesubject to mechanical forces. Dissolution occurs when materials at thesurface contact chemicals in the slurry and become subject to chemicalor electrochemical reactions.

In one embodiment, the slurry may include an abrasive and a complexingagent. The abrasive may include particles, such as Alumina (Al₂O₃) orSilica (SiO₂), while the complexing agent may include a chemical, suchas Ammonium Hydroxide (NH₄OH) or Potassium Hydroxide (KOH). A relativelysoft pad may be used to prevent the generation of defects. A final buffmay be used to remove scratches.

In a first embodiment, the CMP process involves three polishes. Thefirst polish removes most of the overburden of the conductor layer 170.The second polish planarizes the remaining conductor layer 170 over thebarrier layer 115. The polish rate of the conductor layer 170 in thefirst polish and the second polish may be selected from a range of about90-1,300 nm/minute. The third polish removes the portion of the barrierlayer 115 over the upper surface 117 of the ILD 110 film.

In a second embodiment, the CMP process involves two polishes. The firstpolish removes all of the overburden of the conductor layer 170 andplanarizes the conductor layer 170 over the barrier layer 115. Thesecond polish removes the portion of the barrier layer 115 over theupper surface 117 of the ILD 110 film.

In a third embodiment, the CMP process involves one polish to remove allof the overburden of the conductor layer 170 and remove the portion ofthe barrier layer 115 over the upper surface 117 of the ILD 110 film.

The CMP process should not cause the ILD 110 to fracture or delaminatedue to excessive stress. After the CMP process, an upper surface 177 ofthe inlaid interconnect 175 should be approximately flat and level withthe upper surface 117 of the ILD 110 film.

After planarization with CMP, an etch stop layer may be formed over theupper surface 177 of the inlaid interconnect 175 and the upper surface117 of the ILD 110 film. In some cases, the etch stop layer may alsoserve as a capping layer to prevent diffusion, intermixing, or reactionof the inlaid interconnect 175 with the surrounding materials.

A process sequence analogous to the embodiment shown in FIG. 1 A-F maybe repeated to form the next higher layer of inlaid interconnect. In adual Damascene scheme, each layer includes a via and an overlyingtrench. The total number of layers of interconnect may depend on whetherthe device 95 is a memory device or a logic device. The total number oflayers of interconnect may also depend on the design rules for thedevice 95. In an embodiment of the present invention, a total of 7-10layers may be formed for a logic device with 65-nm design rules.

The present invention also discloses a structure 200 having aninterlayer dielectric (ILD) 110 film that includes diamond-like carbon(DLC), an opening located in the DLC; and an inlaid interconnect 175located in the opening. The ILD 110 film may include a compositedielectric film, such as the DLC. In an embodiment of the presentinvention, the DLC in the ILD 110 film may have a thickness of about100-500 nm. The opening may include a via with an overlying trench. Theinlaid interconnect 175 may include a metal, such as copper, or analloy. An embodiment of the present invention is shown in FIG. 1 F.

The DLC may include pores 112. In an embodiment of the presentinvention, the total porosity, or void fraction, of the DLC may be about0.15-0.30. In another embodiment of the present invention, the totalporosity of the DLC may be about 0.30-0.45. In still another embodimentof the present invention, the total porosity of the DLC may be about0.45-0.60. In yet another embodiment of the present invention, the totalporosity of the DLC may be about 0.60-0.75.

The pores 112 in the DLC may be closed, interconnected, or open. In anembodiment of the present invention, closed pores may be small with anequivalent diameter of about 2-6 nm. In another embodiment of thepresent invention, closed pores may be medium with an equivalentdiameter of about 6-18 nm. In still another embodiment of the presentinvention, closed pores may be large with an equivalent diameter ofabout 18-55 nm.

In an embodiment of the present invention, the porous DLC may have a kvalue of about 2.5 or lower. In another embodiment of the presentinvention, the porous DLC may have a k value of about 2.0 or lower. Instill another embodiment of the present invention, the porous DLC mayhave a k value of about 1.5 or lower.

In an embodiment of the present invention, the porous DLC may have aYoung's modulus of elasticity of about 25 GPa or higher. In anotherembodiment of the present invention, the porous DLC may have a shearstrength of about 15 Gpa or higher. In another embodiment of the presentinvention, the porous DLC may have a high fracture toughness.

Many embodiments and numerous details have been set forth above in orderto provide a thorough understanding of the present invention. Oneskilled in the art will appreciate that many of the features in oneembodiment are equally applicable to other embodiments. One skilled inthe art will also appreciate the ability to make various equivalentsubstitutions for those specific materials, processes, dimensions,concentrations, and so forth, described herein. It is to be understoodthat the detailed description of the present invention should be takenas illustrative and not limiting, wherein the scope of the presentinvention should be determined by the claims that follow.

Thus, we have described a method of forming an electrically insulatingmaterial with low dielectric constant and good mechanical strength and astructure including a dielectric having low dielectric constant and goodmechanical strength.

1. A structure comprising: a substrate; a porous diamond-like carbon(DLC) film disposed over said substrate, said porous DLC film comprisingodd layers with no pores and even layers with pores, said pores beingclosed pores, said pores filled with nitrogen, said nitrogen to reduceintrinsic stress in said porous DLC film wherein an odd layer is at atop of said porous DLC film and said intrinsic stress is compressive; anopening disposed in said porous DLC film; and a conductor disposed insaid opening.
 2. The structure of claim 1 wherein said porous DLC filmcomprises a total porosity of about 0.60-0.75.
 3. The structure of claim1 wherein said porous DLC film comprises closed pores with an equivalentdiameter of about 2-6 nm.
 4. The structure of claim 1 wherein saidporous DLC film comprises a thickness of about 100-500 nanometers. 5.The structure of claim 1 wherein said porous DLC film comprises a kvalue of about 1.5 or lower.
 6. The structure of claim 1 wherein saidporous DLC film comprises a Young's modulus of elasticity of about 25GigaPascals or higher.
 7. The structure of claim 1 wherein said porousDLC film comprises a shear strength of about 15 GigaPascals or higher.8. The structure of claim 1 wherein said porous DLC film comprisesdiamond forms of carbon.
 9. The structure of claim 1 wherein said porousDLC film comprises non-diamond forms of carbon.
 10. The structure ofclaim 1 wherein said porous DLC film comprises aromatic carbon rings andmulti-membered carbon rings.
 11. The structure of claim 1 wherein saidDLC film comprises discontinuities, voids, and defects.